Poly(alkylene carbonate) is an easily biodegradable polymer, and is useful as, for example, an adhesive agent, a packaging material, or a coating material. A method for preparing poly(alkylene carbonate) from an epoxide compound and carbon dioxide is highly eco-friendly in that phosgene, which is a poisonous compound, is not used and carbon dioxide is cheaply obtained.
Many researchers have developed various types of catalysts in order to prepare poly(alkylene carbonate) from an epoxide compound and carbon dioxide since 1960s. The present inventors recently disclosed a highly active and highly selective catalyst synthesized from quaternary ammonium salt-containing Salen [Salen; ([H2Salen=N,N′-bis(3,5-dialkylsalicylidene)-1,2-ethylenediamine]-type ligand [Bun Yeoul Lee, Korean Patent Registration No. 10-0853358 (2008 Aug. 13); Bun Yeoul Lee, Sujith S, Eun Kyung Noh, Jae Ki Min, Korean Patent Registration No. 10-2008-0015454 (2008 Feb. 20); Bun Yeoul Lee, Sujith S, Eun Kyung Noh, Jae Ki Min, PCT/KR2008/002453 (2008 Apr. 30); Eun Kyung Noh, Sung Jae Na, Sujith S, Sang-Wook Kim, and Bun Yeoul Lee, J. Am. Chem. Soc. 2007, 129, 8082-8083 (2007 Jul. 4); Sujith S, Jae Ki Min, Jong Eon Seong, Sung Jae Na, and Bun Yeoul Lee, Angew. Chem. Int. Ed., 2008, 47, 7306-7309 (2008 Sep. 8)]. The catalyst disclosed by the present inventors exhibits high activity and high selectivity, and allows the preparation of a copolymer having a large molecular weight. Also, polymerization thereof is possible even at a high temperature, and thus, the catalyst can be applied in a commercial process. In addition, since a quaternary ammonium salt is contained in the ligand, the catalyst can be easily separated from the copolymer after a copolymerization reaction of carbon dioxide/epoxide and reused.
In addition, the present inventors carefully analyzed, particularly, the structure of a catalyst exhibiting high activity and high selectivity as compared with others among a catalyst group of the patent, and then found that the catalyst has a particular structure not known in the literature, in which a nitrogen atom of the Salen-ligand is not coordinated but only oxygen atoms are coordinated to a metal (see, Structure 1 below, Sung Jae Na, Sujith S, Anish Cyriac, Bo Eun Kim, Jina Yoo, Youn K. Kang, Su Jung Han, Chongmok Lee, and Bun Yeoul Lee, “Elucidation of the Structure of A Highly Active Catalytic System for CO2/Epoxide Copolymerization: A Salen-Cobaltate Complex of An Unusual Binding Mode” Inorg. Chem. 2009, 48, 10455-10465).

In addition, there was developed a method of easily synthesizing the ligand of Structure 1 above (Min, J.; Seong, J. E.; Na, S. J.; Cyriac, A.; Lee, B. Y. Bull. Korean Chem. Soc. 2009, 30, 745-748).
The compound of Structure 1, which is a highly-active catalyst, is used to prepare poly(alkylene carbonate) having a high molecular weight economically. The polymer obtained in this case has a molecular structure of a complete alternating copolymer of carbon dioxide and epoxide.
The preparation of a polymer containing a predetermined amount of ether linkages of such as Molecular Structure 2 below through the carbon dioxide/epoxide copolymerization reaction is useful. The polymer chain exhibits flexibility by including ether linkages, thereby lowering the glass transition temperature of resin, and thus, the polymer can be useful for soft plastics. Further, it has been reported that poly(alkylene carbonate) containing ether linkages is soluble in supercritical carbon dioxide, and thus may be used as a surfactant in this fluid (Nature, 2000, vol 404, 165).

Catalysts for preparing poly(alkylene carbonate) containing ether linkages at the time of a carbon dioxide/epoxide copolymerization reaction has been reported. The present inventors have reported that poly(cyclohexene carbonate)s containing 15 to 75% of ether linkages were prepared when carbon dioxide and cyclohexene oxide were polymerized by using an anilido-aldimine zinc compound substituted with plural fluorines as a catalyst (Inorg. Chem. 2006, 45, 4228-4237). However, this has limitations that catalytic activity was low (TOF <1500 h−1) and also the reaction proceeds only when the epoxide compound is cyclohexene oxide, and thus, industrial usefulness thereof is less. When a zinc glutarate based heterogeneous catalyst is used, there is obtained poly(alkylene carbonate) containing ether linkages of below 10% (Polymer Reviews, 2008, 48, 192).
A double metal cyanide (DMC) catalyst is most useful in preparing polyether by ring-opening polymerization of epoxide. The DMC catalyst is a term commonly used in general documents and published patents, and many patents related to methods for preparing the DMC catalyst and methods for preparing polyether using the DMC catalyst are disclosed [e.g., US Patent Publication No. 2008/0167502 (BASF); US Patent Publication No. 2003/0158449 (Bayer); US Patent Publication No. 2003/0069389 (Shell); US Patent Publication No. 2004/0220430 (Repsol Quimica); U.S. Pat. No. 5,536,883 (1996, Arco); and US Patent Publication No. 2005/0065383 (Dow)].